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Description of a Reed Switch
By Tab Hauser
A Reed Switch is a simple, electronic, switching device that
uses two pieces of wire to create a Form A style or three
pieces of wire to create a Form C. Hasco’s reed switch
blades are specially produced and sealed in a glass tube
and then placed in an inert gas. The advantage of using Hasco’s
brand is that you are unlikely to come across any contact
resistance build-up over years of use or more important “non-use” because
the blades are sealed off from outside elements.
Reed switches are commonly used with magnets to open or close
a circuit. An example of their use would be the alarm sensor,
known as a magnetic contact, on doors or windows. Another
popular application for their use is in liquid level sensors
where the reed switch is stationary on a wall and the magnet
is on a float that moves up and down.
Reed Switches are also used in relay applications. To make
a reed relay, a reed switch is covered with a coil that creates
a magnet when the coil is energized which then closes the
circuit. A reed relay is different from a general purpose
relay in that the regular relays do not have their contacts
sealed in glass. Hasco’s general purpose relays switch
current above 1 amp while most reed
relays switch current
from very low levels to about 2 amps.
An advantage of a reed switch is its long life at low current.
Hasco’s products have been tested in hundreds of millions
of cycles. More important than having a reed go on and off
is having it still work after many years of inactivity. This
is critical in life safety applications.
Hasco has over a dozen styles in various sensitivities or
what is called ampere turns. The lower the ampere turn, also
known as AT, the more sensitive the reed switch.
It should be noted that Hasco has the capability of selling
reed switches in different ways. We have the capacity to
cut and bend our product to most PCB specifications. Hasco
can customize our switches for surface mount applications
as well. Lastly, Hasco reed switches can be sold in tape
and reel for auto insertion.
Below is a picture of a Form A Hasco Reed Switch
For a description on how magnetic contacts work, please go
to
http://www.tanealarm.com/magnetic_contacts_101.asp
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